This invention relates to a method of producing a semiconductor device and to a semiconductor device produced by the invented method.
Appended FIG. 1 shows a prior method of producing a semiconductor device, for example, a diode. As shown in FIG. 1A, a SiO.sub.2 film (2) is selectively formed on the surface of an N-conductivity type silicon substrate (1). The SiO.sub.2 film (2) is formed by, for example, thermally oxidizing the silicon substrate (1), followed by selectivily removing the SiO.sub.2 film by a photo-etching technique so as to provide an opening (3). Then, a P-conductivity type doped oxide film (4), such as a silicon dioxide film containing an acceptor impurity, is formed over the entire exposed surface of the substrate (1) and the SiO.sub.2 film (2) as shown in FIG. 1B. When the laminated body thus obtained is heat-treated, the acceptor impurity contained in the doped oxide film (4) is diffused into the substrate (1) so as to form a P-conductivity type region (5) within the substrate as shown in FIG. 1C. As the result, a p-n junction is formed within the substrate. Finally, part of the doped oxide film (4) disposed on the P-conductivity type region (5) is removed by a photo-etching technique so as to allow part of the region (5) to be exposed to the atmosphere and, then, a metal film (6) acting as an electrode is formed as shown in FIG. 1D. It is seen that the metal film (6) is in direct contact with the P-conductivity type region (5) and extends over the SiO.sub.2 film (2) and the doped oxide film (4). Incidentally, the reference numeral (7) shown in FIG. 1D denotes a metal film (electrode) connected to the N-conductivity type region of the substrate (1). The metal film (7) is formed in substantially the same manner as for forming the metal film (6).
In the prior method described, part of the doped oxide film (4) is removed prior to the formation of the metal film (6) by a photo-etching technique to allow part of the P-conductivity type region (5) to be exposed to the atmosphere. In this step of removing the film (4), a mask of an extremely small pattern for photo-etching is used. This presents a difficulty; when the mask is brought in contact with the photoresist film formed on the doped oxide film (4), a slight deviation inevitably occurs in the location of the mask. The deviation problem is serious particularly where a semiconductor device, for example, a diode is incorporated into an integrated circuit device requiring a pattern of high accuracy.
Appended FIGS. 2A and 2B are intended to explain the inconveniences caused by the deviation problem in question. To be more specific, FIG. 2A shows a case where the doped oxide film (4) disposed on the P-conductivity region (5) has been removed as desired by using a mask for photo-etching, thereby providing an opening (21) satisfactorily. In contrast, FIG. 2B shows a case where the doped oxide film (4) and the SiO.sub.2 film (2) have been undesirably etched away because of the deviation in location of the mask. In this case, it is seen that a p-n junction (22) is exposed to the atmosphere. Incidentally, the members equal to those shown in FIG. 1 are denoted by the same reference numerals in FIGS. 2A and 2B. If the p-n junction (22) is exposed to the atmosphere as shown in FIG. 2B, a serious problem is presented. As described previously, a metal film acting as an electrode is formed in the succeeding step in contact with the etched region of the substrate. It follows that the P and N regions of the substrate are short-circuited.
The prior method described utilizes a heat treatment at a high temperature so as to diffuse an impurity into a substrate of one conductivity type, thereby forming a region of the other conductivity type within the substrate. This presents an additional difficulty. Namely, the heating at a high temperature causes a number of lattice defects within the crystal of the substrate. In addition, it is difficult to control accurately the shape of the diffusion region, particularly, the width and depth of the region formed by the diffusion technique.